Lateral mobility and organization of cell surface molecules are important in normal cell functions, for example, response of receptors to their ligands and presentation of antigens to T cells. Even the general principles of lateral organization of membranes are not well understood. Our work concentrates on the mobility and associations of class I MHC antigens. These properties of the antigens appear to be affected by the organization of membranes into domains, and by the extent of glycosylation of membrane proteins. We will characterize lateral diffusion of the antigens in glycosylation-defective mutant cells and will use both fluorescence photobleaching and digital video microscopy to characterize the spatial organization of a variety of class I antigens in fibroblasts and lymphocytes. We will use flow cytometric measurements of quenching of Terbium-labeled antibodies to determine local diffusion coefficients and to select variants in lateral diffusion for function studies. The function of class I antigens in antigen presentation will be investigated by measuring energy transfer between class I antigens labeled with fluorescent beta-2m and fluorescent viral antigens. Differences in the mobility of class I antigens in different lymphocyte subsets will also be investigated.